BISABOLENE EPOXIDES IN SEX-PHEROMONE IN NEZARA-VIRIDULA (L) (HETEROPTERA, PENTATOMIDAE) - ROLE OF CIS ISOMER AND RELATION TO SPECIFICITY OF PHEROMONE

The trans- and cis-(Z)-alpha-bisabolene epoxides (trans- and cis-(Z)(-alpha BE) are the main components of the male sex pheromone in Nezara viridula. The role of the cis isomer and the importance of the cis/trans proportion for the activity and the specificity of the pheromone are not clearly elucidated and were studied here, Interindividual variation of the cis/trans proportion produced by males was studied by individual hexanic extracts in two strains originating from the south of France (SF) and French West Indies (FWI). The trans isomer composed 42-82% of bisabolene epoxides in SF males and 74-94% of bisabolene epoxides in FWI males. Means (+/- SD) significantly differ between SF (62.8% +/- 8.4) and FWI (82.4% +/- 5.9) males in spite of this interindividual variation. Different isomers of bisabolene epoxide were synthesized and their EAG activity on female antennae was compared. Racemic trans- and cis-(Z)-alpha BE elicited low EAGs, not different from the nonnatural trans and cis (E)-alpha BE that were inactive on behavior. Behavioral tests revealed that racemic trans- and cis-(Z)-alpha BE attracted 45% (P < 0.05) and 25% (P < 0.05) of females, respectively. The same levels of attraction were obtained with (-) enantiomers of trans- and cis-(Z)-alpha BE, which attracted 40% (P < 0.05) and 20% (P > 0.05) of the females, respectively. Binary blends containing 75/25, 50/50, and 25/75 proportions of cis/trans isomers were more attractive than trans-(Z)-alpha BE alone and response of females to the 25% cis/75% trans blend was significantly more important than the response to transisomer alone (P < 0.05). The importance of the cis/trans proportion in relation with the specificity of the male pheromone is discussed.